Implantable medical devices are employed to restore the normal function of the human body. For example, some devices are placed within a conduit located within the human body to restore the patency of the conduit. Other devices serve orthopedic functions such as replacing or repairing joints or bones. These devices include, without limitation, stents, catheters, sutures, meshes, vascular grafts, shunts, filters for removing emboli, artificial hips and bone anchors. Stents are generally a mesh tubular structure that is placed within a vessel. Stents are percutaneously placed within the vessel whereby the stent has a first compressed shape for passage through the vasculature of the patient to a targeted area where it is necessary to restore the patency of the vessel. Once at the targeted area the stent is expanded into a second shape, usually after the area has already been subject to a procedure, such as angioplasty, that opens the lumen of the vessel. Once the stent is expanded the lumen of the vessel is remodeled restoring adequate blood flow through the vessel.
A stent located within a vessel often stimulates reactions that result in the formation of clots (thrombosis) or smooth muscle tissue proliferation (restenosis) that causes the lumen to constrict. In order to avoid these complications, a variety of stent coatings and compositions have been proposed that limit adverse reactions. For example, certain coatings reduce the stimulus the stent provides to the injured lumen wall, thus reducing the tendency towards thrombosis or restenosis. Alternately, the coating may deliver a pharmaceutical/therapeutic agent or drug to the lumen that reduces restenosis. Typically, the therapeutic agent is embedded within the matrix of a polymer coating that is applied to the stent. The agent is delivered via diffusion through a bulk polymer, through pores that are created in the polymer structure, or by erosion of a biodegradable coating. It is necessary to ensure that the proper amount of agent is delivered to the targeted area. In order to deliver the therapeutic agent in a predictable manner it is necessary to ensure that a polymer will permit proper elution.
Both bioabsorbable and biostable polymeric compositions have been used as coatings for stents that will provide a stable platform for the predictable delivery of a therapeutic agent. These are generally polymeric coatings that either encapsulate a pharmaceutical/therapeutic agent or drug, e.g. taxol, rapamycin, etc., or bind such an agent to the surface, e.g. heparin-coated stents. These coatings are applied to the stent in a number of ways, including, though not limited to, dip, spray, or spin coating processes. One class of biostable materials that has been reported as coatings for stents is fluorous homopolymers. Polytetrafluoroethylene (PTFE) homopolymers. These homopolymers, however, are not soluble in any solvent at reasonable temperatures and therefore are difficult to coat onto small medical devices while maintaining important features of the devices (e.g. slots in stents).
Another approach has been to employ coatings made from poly(vinylidene fluoride) homopolymers and containing pharmaceutical/therapeutic agents or drugs for release have been suggested. Like most crystalline fluorous homopolymers, however, these are difficult to apply as high quality films onto surfaces without subjecting them to relatively high temperatures, e.g. greater than about 125-200° C., that correspond to the melting temperature of the polymer.
One approach to providing a more stable platform is disclosed in U.S. Pat. No. 6,746,773—Llanos that discloses methods and composition for biocompatible coatings and films. These coatings are used on implantable medical devices and medical devices comprising such coatings and films applied to a surface thereof that is to be in contact with body tissue of a mammal. The biocompatible film provides an inert surface to be in contact with body tissue of a mammal upon implantation of the device in the mammal. The coating and film comprise a film-forming fluorous copolymer comprising the polymerized residue of a first moiety selected from the group consisting of vinylidene fluoride (VDF) and hexafluoropropylene (HFP).
It would be advantageous to develop additional fluorous coatings for implantable medical devices that offer a wider range of hydrophobicity and better mechanical properties. This will allow the coating to reduce thrombosis, restenosis, or other adverse reactions, that may include, but do not require, the use of pharmaceutical or therapeutic agents or drugs to achieve such affects. The coating will also possess physical and mechanical properties effective for use at relatively low maximum temperatures. It would also be advantageous to develop additional fluorous coatings with various physical properties to meet delivery parameters of a wide-range of pharmaceutical agents.